Targeting a nested mc timeline

I have a main.fla which has 3 movieclips inside it. All 3 mc’s have timelines that run 40 frames. The main.fla timeline has each mc instance on a frame.

mc_1 is on frame 1
mc_2 is on frame 40
mc_3 is on frame 81

as the main timeline plays the clips each one fades to the other.

I need to know how to target this scenerio

after mc_3 plays I need to have a goToAndplay (20) set up so the animation inside mc_1 starts playing (frame 20) of mc_1.
the action needs to happen when the playhead reaches the last frame of the main timeline in main.fla

any help?

rdefr